Muscle activity is regulated by the cytoplasmic Ca2+ concentration. Contraction initiated by Ca2+ release from the sarcoplasmic reticulum while relaxation follows the reaccumulation of the Ca2+ by the sarcoplasmic reticulum. Ca2+ release is activated by an unknown mechanism following depolarization of the action potential. Ca2+ transport into the sarcoplasmic reticulum is mediated by the Ca2+, Mg2+-ATPase. The purpose of this research project is to investigate several functional properties of isolated sarcoplasmic reticulum vesicles and T-tubule vesicles in order to increase our understanding of how the cytoplasmic Ca2+ concentration is regulated in the muscle fiber. We would like to investigate: 1. The relationship between Ca2+ and H+, K+ and potential gradients across the sarcoplasmic reticulum membrane. 2. The mechanism by which calsequestrin (a Ca2+-bindidng protein in the sarcoplasmic reticulum lumen) aggregates. 3. The mechanism of Ca-induced Ca release. 4. The structure and function of the voltage-gated Ca2+ channel of the T-tubule. The ultimate goal of this research is to establish an in vitro system to study excitation-contraction coupling.